I want to set up a 3 monitor display but I am fairly certain my gfx card only supports 2 monitors so I decided that SLI is my best option to add a third (I currently use 2). I know that normally you need 2 of the same cards for SLI but will I need to get the same MSI card that I have now (see link above) or can a get a different GTX 550 TI like this or this?
If you are gaming I would highly suggest you stay away from SLIing those 2 cards, they are very weak. If you want to then you could, they just have to have the same amount of VRAM last time I checked. You can mismatch brands, anything but VRAM.
from reviews I have read the cards should be able to handle most things SLIed and since one has been able to handle 2 monitor gaming fine on high settings (just tired of the damn bezel) i figure two could handle 3 monitors
If you are going to game on multi monitor (which was what I meant by poor performance) then it will not work well. They are limited to 1gb of ram and if you have high resolutions you will need A LOT more ram than just 1gb.